I. Field of the Invention
This invention relates generally to a solar concentrator. In particular, the present invention relates to simple, lightweight, and inexpensive reflector panels comprising reflective surfaces of excellent optical quality. The invention also relates to an assembly comprising a plurality of reflector panels arranged on and secured to a contoured support frame assembly. The invention also relates to the use of this assembly to reflect and concentrate incident radiation onto a reference surface.
II. Background of the Related Art
A solar concentrator operates by intercepting incoming solar radiation and redirecting it to a concentrated region where it is changed into a useable form of energy that can be applied to meet a specific demand. Energy harvested in this manner is known as concentrated solar power (CSP) and it is currently more efficient than photovoltaic cells at converting solar radiation into electricity. Another advantage of CSP is that it can also supply process heat and power while tracking the sun. The amount of energy generated by a solar concentrator depends on its efficiency which, in turn, is determined by how it is constructed, its configuration, and the choice of materials used. The key and, frequently, one of the most expensive components in a solar concentrator is the reflective surface which is also referred to as a solar mirror. There are three generic types of solar mirrors: heliostats, parabolic troughs, and solar dishes. These are known as central receiver type, line focus type, and point focus type solar mirrors, respectively.
Heliostats are substantially flat reflectors which concentrate sunlight onto raised focal point receivers. An example of a heliostat comprising reflector elements and carriers which support the reflector elements above a ground plane is disclosed in U.S. Patent Publ. No. 2004/0074490 to Mills, et al. which is incorporated by reference as if fully set forth herein. Heliostats are disadvantageous in that they have stringent mirror contour requirements as well as the added expense of tall towers which are needed to support the remote receivers. Parabolic troughs are one of the most commonly used solar reflectors. They are simple-curve parabolic reflectors which concentrate sunlight onto long receiver pipes spanning the full length of the reflectors. The disadvantages of troughs include a low maximum solar concentration, high receiver heat losses, and high receiver costs. Since both heliostats and troughs do not face the sun directly, both suffer from performance losses known as cosine losses. Solar dishes are compound-curve paraboloidal reflectors which concentrate sunlight onto small receivers supported near the centers of dish apertures. Solar dishes generally achieve the highest solar concentrations and the best efficiency since they directly face the sun. However, solar dishes are the most expensive solar reflectors, requiring fabrication of costly compound and complex reflector curves and the use of expensive mirror substrates. Heliostats and solar dishes also require dual axis optical tracking capabilities.
Although the different types of solar mirrors discussed above may be advantageous for specific purposes, their complexity, stringent design requirements, and comparatively high cost are barriers to their widespread implementation as solar concentrators. The additional cost considerations arise primarily from the complexity associated with their fabrication and use. Some further examples include the need for molding substrates to control mirror curve contours, use of air pressure to deflect reflective membranes, fabrication of structures with a contiguous mirror support for mirror curve shaping, and the implementation of systems to avoid thermal stresses in mirrors due to use of dissimilar structural materials. The complexity of conventional solar mirrors is furthered by the need for motorized solar tracking drives, tracking rails, and pivot bearings.
A variety of approaches have been followed in attempting to simplify some of the additional complexities identified above. An example is U.S. Pat. No. 7,192,146 to Gross, et al. which discloses a ground-based tracking array in which the orientation of all optical elements in the array can be adjusted by a single motor. Another example is provided by U.S. Pat. No. 7,156,088 to Gregg Luconi which discloses a simplified support structure for solar concentrators which may be mounted in areas where penetration of the mounting surface for anchoring purposes is not permitted. Examples of devices which enable tracking of the sun's motion are described in U.S. Pat. No. 6,960,717 to Stuart, et al.; U.S. Pat. No. 6,552,257 to Hart, et al.; and U.S. Pat. No. 6,042,240 to Louis Strieber. Each of the aforementioned patents are incorporated by reference as if fully set forth herein.
Although the above applications each address a number of design issues, the reflective surfaces used in the prior art still suffer from a number of problems. Generally, solar mirrors are formed from either a polished metal sheet or a glass plate which is backed by a reflective film and supported by a metal substrate. An example of a mirror formed from glass having a metallic silver coating deposited thereon is provided in U.S. Pat. No. 4,737,188 which is incorporated by reference as if fully set forth herein. These type of reflective surfaces are generally extremely heavy, are difficult to fabricate to precisely tailored dimensions and, in the case of glass, are susceptible to fracture. An additional issue is that the materials from which the mirror itself is fabricated are generally expensive and are susceptible to corrosion under ambient conditions. In view of the above and other considerations there is therefore a continuing need to develop a simplified and cost-efficient solar concentrator from high-quality reflective elements which are durable, lightweight, and of low cost.